Small robot, big tasks
Mini-Whegs™ are a set of biologically inspired robots that combine the speed and simplicity of wheels with the high mobility of legs. The outline for this project was to redesign and CAD a Mini-Whegs robot for a new specific task.
Understanding the requirements
The redesigned robot would be engineered to travel on snow and ice, operating in cold environments. The robot could assist in safety routines for checking thicknesses of ice, wildlife research and photography, and search and rescue operations. It was given the name Snow-Whegs.
INITIAL DESIGn specification
An initial design was developed as a starting point for the design process, much of which built on a morphological analysis and research of the concepts behind the original Mini-Whegs and similar biomimicry robots.
A rack-and-pinion system was designed to steer the robot.
When cross-country skiers embark inclines they often position their skies both facing outwards, for better traction on the surface. To make the robot perform better on snowy inclines, a similar approach was taken. Using two micro servos, operating two separate racks, the whegs could still be steered normally, but also put in a position both facing outwards.
CUSToMISED UNIVERSAL JOINT
A universal joint was designed to allow for the required degrees of freedom to power and steer the wheels simultaneously.
Interference detection and motion analysis simulations were used to iterate the joint to its final design.
MOTOR AND POWER SUPPLY selection
The contact point between the whegs and an obstacle to overcome was used to derive the equation for the required torque the motor. A 6 V C geared motor motor was chosen, with a power of 2.4 W, speed of 100 RPM, torque of 90 mNm. Two flat lithium-polymer batteries were placed in the top lid, powering the robot for almost 4 hours.
The speed of the selected motor was lower than what required by the brief. A transmission ratio was calculated to increase the speed to the required 120 RPM. For DC motors, the torque decreased as the speed increased, but in this case, it was still higher than required.
It was looked to sports equipment like crampons and snow shoes for inspiration, when re designing the whegs. The wider whegs allows for a bigger surface area on the snow for the robot to distribute its weight. The spikes improve the traction when travelling on ice.
FEA was used to minimise material and weight.
Special equipment, such as cameras and sensors, would be mounted on the Snow-Whegs for its specific tasks.
Components were cut out to dimensions in pieces of paper, to get an understanding of how they could fit together.
The motor was placed in the middle of the chassis, to allow for the same type of belt to be used for both transmissions, and to localize the robots centre of mass.
The overall weight of the Snow-Whegs is approximately 222 𝑔 with an estimated cost of £91.93.
The motor is one of the biggest contributors to both weight, cost and size, and would therefore be a component probable to replace.